1. Technical Field
The present disclosure relates to image registration and, more specifically, to registration of CT volumes with fluoroscopic images.
2. Discussion of Related Art
Electrophysiology (EP) is the study of the electrical properties of the human body. In EP, electrodes are placed in contact with the tissue being observed and changes in electrical potential or current flow are observed. One particular example of EP, the human heart is catheterized with electrodes for monitoring and/or influencing electrical signals that control the beating of the heart.
Catheterization is an invasive procedure in which the catheter electrode is inserted into the heart. One particular example of catheterization is catheter ablation. Catheter ablation may be used to treat arrhythmia in a patient's heart. In catheter ablation, faulty electrical pathways are removed from the heart by advancing ablation catheters through the patient's blood vessels towards the heart. High-frequency electrical impulses are then used to induce the arrhythmia, and then ablate the abnormal tissue that is responsible for the arrhythmia.
Catheterization, for example, for the purposes of catheter ablation, is generally only performed in expensive and highly specialized facilities known as catheterization laboratories or cath labs. During catheterization, the patient is injected with a radio-contrast agent and a fluoroscopy is used to image the vessel structure. While viewing the fluoroscopy images, catheterization may be performed by inserting the ablation catheter through the vessel structure to the patient's heart.
The fluoroscopy used in catheterization is generally a two-dimensional x-ray fluoroscopy that is capable to providing real-time monitoring of the catheter as it travels through the vessel structure and enters the patient's heart. The two-dimensional x-ray fluoroscopy may not be able to show soft-tissue structures such as the atriums, the ventricles, the aorta, and the pulmonary veins, and thus navigation of the targeted area may be difficult.
To provide better visualization, the fluoroscopy image data may be registered to high-quality three-dimensional CT image data that was taken prior to the catheterization procedure. The doctor may then be able to view combined image data where the soft-tissue detail of the CT image is overlaid with the real-time fluoroscopy image.
Existing techniques for registering the two-dimensional fluoroscopy image data with the three-dimensional CT image data to a single coordinate system involve injecting radio-contrast into the vessels of interest so that the vessels are clearly visible within the fluoroscopy image. Landmark-based registration is then performed to register the images of the two modalities. In this approach, key landmarks must be manually identified within the three-dimensional CT image data. The same landmarks must then be identified within the two-dimensional fluoroscopy image data so that registration may be performed. The manual selection of landmarks may be laborious and prone to error. Moreover, because the dose of radio-contrast must be limited sue to safety concerns, the ability to identify the landmarks within the fluoroscopy image data is limited.